Internal combustion engines in which one group of cylinders is operated permanently and another group of cylinders can be deactivated are generally known. In a two-bank engine concept with cylinder deactivation, it is possible, when a bank is deactivated, for an associated catalytic converter to cool down. The conversion rate falls considerably as a result.
DE 4431058 C1, which is incorporated by reference, discloses an internal combustion engine having a deactivatable cylinder group, which has an exhaust system. The catalytic converter assigned to the deactivatable cylinder group is traversed by flow to such an extent that said catalytic converter does not cool down to too great an extent after the deactivation of the cylinder group, such that it is possible for the catalytic converter to take effect quickly after reactivation of the cylinder group.
If in each case one catalytic converter is arranged in the exhaust lines of the permanently operated cylinder assembly and of the deactivatable cylinder assembly, a bypass line runs between said two catalytic converters and the catalytic converter assigned to the exhaust line of the permanently operated cylinder assembly can, downstream thereof, be entirely or partially blocked or throttled, cooling of the catalytic converter of the deactivatable cylinder group after the deactivation of said cylinder group can be substantially prevented.
The cooling of the catalytic converter assigned to the deactivatable cylinder group can be prevented if the bypass line extends from the exhaust line of the permanently operated cylinder assembly upstream of the catalytic converter assigned to said cylinder assembly, and issues into the exhaust line of the deactivatable cylinder assembly upstream of the corresponding catalytic converter. When the blocking element is completely closed, it is thus possible for the very hot exhaust-gas flow branched off upstream of said catalytic converter to heat the catalytic converter situated in the shut-off exhaust line. When the blocking element is partially closed, it is possible to realize an apportionment of the exhaust-gas flow of the permanently operated cylinder assembly, such that both catalytic converters are impinged on by a partial exhaust-gas flow. Cooling of the catalytic converter of the deactivated cylinder assembly is thus substantially prevented.
A problem in a two-bank engine concept with cylinder deactivation and additional bank-specific supercharging is however the fact that exhaust gas does not flow through the turbine situated on the deactivated bank, and said turbine thus comes to a standstill. This has the effect firstly that the sealing action of the radial shaft sealing rings on the charger shaft is decreased because the seal is ensured only while the rotor is rotating. Secondly, this has the effect that the turbocharger does not deliver a charge pressure upon activation of the inactive bank, which manifests itself in unfavorable response behavior.